1. Field of the Invention
The present invention relates to an improved method for the preparation of crystalline aluminosilicate zeolites.
2. Description of the Prior Art
It is known to produce crystalline aluminosilicates from a reaction mixture comprising a source of silica, a source of alumina, water and an organic templating agent. The resulting zeolite associated with the organic templating agent is calcined to remove the organic moiety and leave a hydrogen cation associated with the anion framework of the zeolite. See, for example, Zeolite Beta described in U.S. Pat. No. Re. 28,341 (reissue of U.S. Pat. No. 3,308,069), Zeolite ZSM-5 described in U.S. Pat. No. 3,702,886, Zeolite NU-1 described in U.S. Pat. No. 4,060,590, the teachings of which are hereby incorporated by reference. Zeolite ZSM-8 is described in British Pat. No. 1,334,243.
It has now been found that less organic templating agent is required to form the organic cation-containing zeolite when a source of organic templating agent is added to a preformed aluminosilicate gel containing a low amount of water and a low alkali metal content.
U.S. Pat. No. 3,578,398 discloses the synthesis of a zeolite similar to offretite. The reactants comprise sodium aluminate, potassium hydroxide, silica hydrosol and tetramethylammoniumhydroxide. In Example 1, colloidal silica is reacted with sodium aluminate and aged. The aged product, a hydrogel, is then reacted with tetramethylammoniumchloride.
U.S. Pat. No. 3,642,434 discloses a method of preparation of ZSM-4. Solutions comprising sodium aluminate, sodium silicate and aluminum chloride are reacted to form a slurry. Tetramethylammoniumhydroxide is then reacted with the slurry.
U.S. Pat. No. 4,046,859 discloses a method of synthesizing ZSM-21. Example 1 shows that solutions comprising sodium silicate, sodium aluminate and aluminum sulfate are reacted to form a gel. The gel is mixed with 2-hydroxyethyl trimethylammoniumchloride. The mixture is crystallized to form a zeolite.
U.S. Pat. No. 3,793,385 discloses a hydrocarbon separation process in which at least one C.sub.8 aromatic isomer is separated from a mixture of C.sub.8 aromatic isomers using zeolite Beta as sorbent.